1. Field of the Invention
The present invention relates generally to oscillator circuits and, more particularly, to an oscillator circuit using an inductive circuit formed of field effect transistors. The invention has a particular applicability to microwave oscillator circuits using metal semiconductor field effect transistors (MESFETs).
2. Description of the Background Art
In recent years, various small electronic apparatuses utilizing a microwave signal have been developed and supplied for commercial use. Such electronic apparatus includes in general an oscillator having an oscillation frequency of a microwave band, i.e., a microwave oscillation circuit. Recently, with advancement in down-sizing of electronic apparatus, it is desirable that an occupied area of a microwave oscillation circuit on semiconductor substrate is reduced. The present invention is in general applicable to oscillator circuits using field effect transistors. A description will now be made on an example in which the present invention is applied to a microwave oscillation circuit employing metal semiconductor field effect transistors (hereinafter referred to as MESFETs).
FIG. 3 is an equivalent circuit diagram of a conventional microwave oscillation circuit. With reference to FIG. 3, this oscillation circuit includes a field effect transistor 70, an inductor 72 and a capacitor 73 both connected to a source (S) of transistor 70 through a transmission line 75, an output load resistor 74 connected to a drain (D) of transistor 70, and an inductor 71 connected to a gate (G) of transistor 70. Since transistor 70 has its gate grounded through inductor 71, a circuit having negative resistance in a desired frequency band can be structured when viewed from the source of transistor 70. Since inductor 72 and capacitor 73 together constitute a parallel resonance circuit, an oscillation circuit is formed by setting transmission line 75 under phase conditions satisfying oscillating conditions for negative resistance.
In a microwave band, it is very difficult to implement an inductor of a concentrated constant for forming such an oscillation circuit. Thus, inductance as a resonance element is normally constituted by using transmission line 75. The oscillation circuit of this type is widely used because of its simple structure; however, an increase in the size of the circuit is unavoidable because of usage of transmission line 75.